ZnSe quantum dots within CdS nanorods: a seeded-growth type-II system.

The sizeand shape-dependent optical properties of colloidal semiconductor nanocrystals can be enhanced significantly by the growth of heterostructures of at least two materials. The potential profile of the involved materials dictates the optical properties of the final structure, where the most common typeI alignment has been extensively used in spherical core/shell nanocrystals to achieve electron and hole confinement in the core leading to high photoluminescence quantum efficiencies and enhanced stability. Type-II alignment, where the potential profile leads to charge-carrier separation, has also been reported and leads to prolonged emission lifetimes, modified multiexciton behavior, and enhanced optical-gain characteristics. Anisotropic rod heterostructures are also of great interest, and previously advantageous optical-gain studies were reported for type-I core/shell rods. Heterostructures were also grown by combining different materials into the growing nanorod. In particular, type-II nanorod heterostructures of CdSe/CdTe showing light-induced charge separation were recently reported. Exceptional optical properties and uniformity were recently reported for CdS nanorods with CdSe seeds by Talapin and Manna. A seeded-growth approach was utilized, based on earlier work on this system, which has already yielded significant insight to the electronic structure and optical properties of type-I seeded dot–rod heterostructures. Here, we expand this synthetic approach and develop CdS nanorods with embedded ZnSe quantum dots, which constitute an example of a nanorod heterostructure with a seed of zinc blende crystal structure. This structure is of high interest because of the type-II potential profile characteristics of ZnSe and CdS (see Figure 1). According to this potential profile, a charge-carrier separation should occur in the excited state of